Many aspirating diluter/dispenser devices are known. Such devices often have a hand held probe which is used as a pipette to measure predefined amounts of a sample, then dilute that sample with a predefined amount of a reagent and finally dispense the reagent and/or sample, after having accomplished reasonably accurate and precise measurement of the sample and/or the sample and reagent. Such devices often use replacable tips which contain chambers carrying the reagent and/or sample so as to space the samples from a central liquid supply in the chamber. Often a variety of tips having different sized chambers are used to meter and dispense different volumes of a sample.
The different sized tips are required, since the devices are aspirating devices and if large air spaces are left in a tip when measuring small quantities for example, this can introduce errors in measurement and/or give difficulty in aspirating and dispensing.
Thus, it is well known that a dead air space between a vacuum or positive pressure creating mechanism, like a syringe or a piston, can cause an increase in liquid volume pickup or delivery. For this reason, sampling tips or tubes on probes are designed to be filled with liquid sample and/or reagent used to eliminate large air spaces, since liquid is, for all practical purposes, incompressible, unlike gases such as air.
Conventional disposable tips are often formed of plastic and made disposable to avoid contamination between one sample and another. It is often desired that the sample is picked up and confined to the disposable tip so that no sample actually gets into a hand held probe used in measuring and dispensing devices, to eliminate possible contamination of the device.
The need for contamination elimination is particularly important in many medical applications, particularly with AIDS or other virus tests and with sensitive tests such as nucleaic acid tests and determinations.
Often very small sample volumes down to one microliter and less, are measured and dispensed in laboratory testings. Often such small samples are diluted with reagents in much larger volumes. It has been difficult to use a standard size, single size disposable tip to handle both the sample and reagent, since often a tip that is large enough to hold reagent and large sample volume will have a dead air space that can cause considerable error in a small sample If the sample size is varied, as from 1 microliter to perhaps 50 microliters in different tests or different procedures, that difference can cause the dead air space to be a problem.